1. Field of the Invention
The present invention relates to a method and system for analysing sound (e.g. music tracks). Tracks from a database of sounds, for example music, can be analysed in order to predict automatically the effect or impact those sounds will have on a listener.
2. Technical Background
It is well established that there are specific levels of neuro-physiological arousal (related to mood, states of mind and affect) best suited to particular activities such as study, relaxation, sleep or athletic performance. However, because these levels of arousal result from complex interactions between the conscious mind, environmental stimuli, the autonomic nervous system, endocrine activity, neurotransmission and basal metabolism, it is difficult to control and sustain them.
It is also well established that there is a universal human response to music based on a complex set of functions ranging from perceptual systems, by way of cerebral cortex and other processing, to activation of core emotional centres of the brain and the somatic systems. It is similarly well established that these functions reside in parts of the brain such as, for example, the cochlea, primary auditory cortex, pre-motor cortex, amygdala and the periaqueductal grey (and so on). Rhythm, for example, has a measurable effect on the pre-motor cortex, autonomic nervous system, somatic systems, the endocrine system and neurotransmission. Other aspects of musical structure and experience may also influence human neurophysiology, as described below.
3. Discussion of Related Art
Three ways are known of analysing music for arousal and counter-arousal using humans (for brevity, the term ‘arousal’ will at times be used to include counter-arousal in this document). The first method entails the judgment of an individual, who might be either an expert or the subject him or herself. The second method is by testing many people and asking them how they feel in response to different music tracks. Neither is reliable because each is too subjective.
The third method is to analyse metrics computed as a function of the music itself (usually tempo, but may also include a measure of average energy), and relate such metrics to the desired state of arousal of the subject. There are several such systems, some of which are cited below. Most rely on either ‘entrainment’ (in the Huygens sense, namely the tendency to synchronise to an external beat or rhythm) or on the association of increased tempo (and in one known case, energy) with increased effort or arousal (and the converse for reduced tempo and energy).
Examples of prior art systems that use music selected according to tempo to manipulate arousal and counter-arousal include U.S. Pat. No. 282,045, U.S. Pat. No. 191,037, U.S. Pat. No. 113,725, U.S. Pat. No. 270,667, WO 151116, U.S. Pat. No. 5,267,942). This art may use beats per minute as calculated to predict entrainment or may, as in U.S. Pat. No. 060,446, modulate tempo in order to improve entrainment. Although this art may be directionally correct, and by extension of Huygens' entrainment principle, it is likely to work to some extent with some repertoire, tempo is both difficult to detect automatically and on its own may best be used to calculate neuro-physiological effect in the limited circumstances where the tempo is both easily and accurately detected and where it is close to the current heart rate of the listener (see next paragraph). Any significant divergence and the entrainment effect is likely to be lost. Most significantly, as discussed below, effective rhythmic entrainment depends on more than beats per minute, and is inseparably synergetic with and dependent on other musical generators of arousal, such as, for example harmonicity and turbulence.
U.S. Pat. No. 5,667,470 relies on the fulfillment or denial of expected outcomes in music in comparison with established patterns in the repertoire, while U.S. Pat. No. 4,883,067 introduces the concept of training the brain to replicate positive patterns of neurological activity by association with certain sound signals. One patent, U.S. Pat. No. 5,267,942, cites the iso-moodic principle documented by Altshuler in 1948 as evidence for its assertion that for the tempo of music to have any effect in entraining heart rate it must lie within the ‘entrainment range’ of the individual's actual heart rate, i.e. close to it. This introduces the notion that the neuro-physiological effect of a piece of music depends on the initial state of the subject, which means that the effect of any given piece of music is relative rather than absolute. Reference may also be made to US 2007/0270667 attempts to use biometric feedback to manipulate arousal.
Reference may also be made to psychoacoustics. Psychoacoustics has been extensively used in music compression technology (e.g. MP3), but another application is documented in U.S. Pat. No. 7,081,579, which describes an approach to song similarity analysis based on seven measured characteristics: brightness, bandwidth, volume, tempo, rhythm, low frequency noise and octave. These techniques can identify ‘soundalike’ music (of which there is much these days) but cannot be used to predict the effect of music in neuro-physiological terms.